809
FXUS63 KLOT 310801
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
301 AM CDT Sun Aug 31 2025

.KEY MESSAGES...

- A pleasant pattern will continue through the holiday weekend.

- An early fall storm system will move through the Great Lakes
  region toward the middle to end of next week accompanied by a
  shot of well below average temperatures.

&&

.DISCUSSION...
Issued at 301 AM CDT Sun Aug 31 2025

A tranquil and pleasant weather pattern will persist through
through Tuesday as high pressure remains dominant across the
Great Lakes region. More sunshine is anticipated today through
Tuesday, which should foster a bit warmer temperatures than what
the area experienced on Saturday. Accordingly, upper 70s are
forecast this afternoon, with readings up around, or just above,
the 80 degree mark on Monday and Tuesday, particularly inland
from the Lake Michigan shore. A persistent onshore easterly wind
will result in a bit cooler temperatures (lower to mid 70s)
along the Lake Michigan lakeshore.

Beyond Tuesday, attention continues to focus on the significant
weather pattern shift expected across North America in response
to the anomalously strong mid/upper-level ridging building
across northwestern Canada. The associated buckling of the Polar
jet over this region will send impulses originating from the
Beaufort Sea south-southeastward across south central Canada,
and ultimately carving out a large upper trough/low over the
Upper Great Lakes region later in the week. There does continue
to be some ensemble spread in regards to the overall strength
and southward extend of the Upper Low into the Upper Great Lakes
late in the week. This spread becomes particularly noteworthy
in regards to the potential for a secondary impulse and
reinforcing shot of cold air to dig into our region along the
western periphery of the upper low on Friday. Nevertheless, the
main message of a period of precipitation with a strong cold
frontal passage late Wednesday into Wednesday evening, followed
by a turn towards much cooler weather by Thursday remains
unchanged.

Robust cold air advection (especially for early September) on
breezy northwest winds will usher in a significant and notable
cool down for Thursday through the end of the week. High
temperatures still look likely to struggle to climb out of the
low to mid 60s on Thursday and Friday as well. For climate
comparison, the record coldest high temperature for Thursday the
4th of September is 60 and 61 in Chicago and Rockford,
respectively. Similarly, overnight low temperatures will be well
below average, and may make a run for the lower 40s (if not
colder) outside of Chicago and away from Lake Michigan.

As noted above, ensemble spread and forecast confidence lowers
Friday into the early part of next weekend. Of particular
forecast interest, is the potential for a secondary impulse and
reinforcing shot of cold air to dive southward into our area on
Friday along the western periphery of the main upper low. If
this potential continues to look increasingly likely, the threat
will be higher for another period of rain showers on Friday
than the current 20% probabilities offered up by the latest NBM.
Temperatures could also end up slower to moderate next weekend.

KJB

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1143 PM CDT Sat Aug 30 2025

No significant aviation weather concerns are anticipated
through the period.

Surface high pressure will remain dominant today over the Great
Lakes region. Accordingly, this will continue to foster light
(10 kt or less) east-northeasterly surface winds through the
period. Otherwise, VFR conditions are anticipated with decreased
cloud cover today and tonight.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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